1. Field of the Invention
This invention relates to a tape path which minimizes the components required to control tape tension, vibrations, and winding disturbances. More particularly, the invention is a tape path having an implicit squeeze bearing.
2. Description of the Related Art
Magnetic tape drives typically use a reel-to-reel tape transport design, or "tape path", for controllably advancing the tape past an adjacent tape head. The tape head includes one or more magnetic transducers for writing to and/or reading from the tape. The tape is wound upon 2 reels, one reel at each end. The tape is advanced by rotation of such reels. One problem in reel-to-reel tape paths is tape velocity and tension variation. Variations in tape velocity and tension cause vibration. Tape vibration can be characterized according to the propagation velocity of the vibratory mode, the length and geometry of the vibration transmission path, and the terminating conditions of the vibration transmission path. Tape vibration modes include shear waves, longitudinal waves, out-of-plane resonant bands, and other path resonances. Such vibration in the tape can disrupt the head-tape interface, and thus effects the overall operation of the drive. PG,4
Existing tape drives control tape tension and vibration in several ways. The IBM 3420 Magnetic Tape Drive and the IBM 3850 Mass Storage Subsystem employ a combination of rollers and vacuum columns for such a purpose. For example, see U.S. Pat. No. 3,912,144. The IBM 3480/3490 Magnetic Tape Subsystem uses a tape tension transducer in a closed loop tension servo control configuration, as disclosed in U.S. Pat. Nos. 4,406,906 and 4,389,600. These and other drives may also use compliant members or tension arms to control tape tension and dampen vibration. U.S. Pat. Nos. 4,456,160, 4,182,472, 3,806,574, 3,175,780, and 3,004,728 disclose various aspects of tape control, such as guiding rollers and flanges. All of the aforementioned controls use devices ancillary to the reels and tape, which adds both expense and complexity to the tape path.
Another problem in reel-to-reel tape paths is air which is entrained in the windings of tape as it is wound upon a reel. The entrained air is trapped into pockets and can result in abrupt tape slippage and changes in tape tension which not only disrupt the head-tape interface, but can also result in catastrophic damage to the tape. The consequences of entrained air depend upon such parameters as the material properties of the tape, the design of the reels and guides used in the tape path, and the winding rate and geometry. Entrained air can be prevented by winding the tape in a vacuum, but such is expensive and inconvenient. U.S. Pat. No. 4,830,303, 4,576,344, and 3,405,884 disclose rollers which are used to control the entrainment of air. Again, rollers are ancillary to the reels and tape and are therefore undesirable. U.S. Pat. No. 3,967,789 also refers to the entrainment of air in a tape winding mechanism.